In a material testing machine capable of performing both a tensile test and a compression test, it is necessary to be able to, on a crosshead, selectively mount a grip, which is a jig used to grip a test piece when performing the tensile test, or a platen, which is a jig used to press a test piece when performing the compression test.
In a conventional material testing machine, a jig mounting device for mounting a grip on a crosshead, and a jig mounting device for mounting a platen on the crosshead are separately prepared, and depending on the content of a test, these jig mounting devices are selectively used. For this reason, when changing a test method from a tensile test method to a compression test method, or from the compression test method to the tensile test method, it is necessary to replace a jig mounting device itself, causing the problems that troublesome work is required and the replacement takes time.
On the other hand, there is proposed a material testing machine including: a load cell that is connected with a grip or a platen through a jig mounting device; a holding member that holds the load cell; and a driving mechanism that applies a load to a test piece between the holding member and a table by moving up or down the holding member, in which the jig mounting device has pin-connected upper and lower members respectively functioning as universal joints, and the upper member is provided with a mounting part for the platen (see Patent Literature 1).
FIG. 5 is a schematic diagram of the conventional jig mounting device described in Patent Literature 1.
In this jig mounting device, the load cell 101 is placed on the upper surface of a crosshead 102 coaxially with a through-hole opening in the crosshead 102. In addition, a screw rod 103 penetrates through the through-hole and the load cell 101, and the load cell 101 is fixed to the screw rod 103 by the action of a lock nut 104 screwed with a screw part formed in a head part of the screw rod 103.
The lower end part of the screw rod 103 is connected with a fork part 105. In the fork part 105, a pin hole insertable with a pin 106 is formed. When mounting a grip (illustration is omitted) for gripping a test piece on the jig mounting device, the grip is mounted on the fork part 105 by inserting a head part formed in the grip into a concave part 107 of the fork part 105, and inserting the pin 106 into a through-hole formed in the head part of the grip. In this case, even in the case where there is a gap between the pin hole formed in the fork part 105 or the through-hole formed in the head part of the grip and the pin 106, the grip is pulled downward at the time of a tensile test, and therefore the gap does not affect the material test.
On the other hand, when mounting a platen 108 on the jig mounting device, as illustrated in FIG. 5, the platen 108 is mounted on the fork part 105 by inserting a head part of a stepped connecting rod 110 attached to a pressing part 109 of the platen 108 into the concave part 107 of the fork part 105, and inserting the pin 106 into the through-hole formed in a head part of the platen 108. Then, a male screw formed on the outer circumferential surface of a large diameter part of the stepped connecting rod 110 is screwed into a female screw formed on the inner circumferential surface of a lock nut 111. After that, by bringing the lock nut 111 into abutting contact with the fork part 105, and drawing the platen 108 toward the pin 106 side by the action of the lock nut 111, the platen 108 is fixed to the fork part 105. In doing so, even in the case where there is a gap between the pin hole formed in the fork part 105 or the through-hole formed in the head part of the stepped connecting rod 110 and the pin 106, the platen 108 can be securely fixed to the fork part 105.